The purpose of this project is to identify and characterize, in an intact cell system, the metabolic processes that determine genotoxicity of known or suspected chemical carcinogens. Emphasis is placed on carcinogenic aromatic amines and amides, and environmental contaminants such as nitrosamines. A sensitive in vitro test system, measuring bacterial mutation frequency and DNA damage in mammalian cells (Salmonella/hepatocyte system), is employed. The research is at present focused on the following areas: (1) the relative roles of metabolic activation and detoxification in determining both the mutagenic and carcinogenic potential of aromatic amines and amides; (2) the relationship between DNA damage, measured by alkaline elution technique, in host cells and the bacterial mutation frequency when known or suspected chemical carcinogens are tested in the Salmonella/hepatocyte system; (3) the regulation of cytochrome P-450 dependent monooxygenase(s) induction during chemical hepatocarcinogenesis; and (4) the modification of both epoxide hydrolase and flavin-dependent monooxygenase activity during chemical hepatocarcinogenesis and the relationship of these enzyme activities with cell growth and differentiation. Results so far obtained include: (1) kinetic analysis of oxidative metabolism of 2-acetyl-aminofluorene (AAF) in liver microsomes from rat, rabbit and human subjects demonstrated that C-hydroxylation (detoxification) is catalyzed by several cytochrome P-450 isoenzymes, whereas N-hydroxylation (toxification) is catalyzed by a single cytochrome P-450 isoenzyme in all three species; (2) metabolic activation of N-acetylarylhydroxamic acids such as N-hydroxy-2-acetyl-aminofluorene and N-hydroxy-phenacetin to genotoxic agents in isolated and intact liver cells from rats and mice occurs via deacetylation; and (3) studies on epoxide hydrolase in both intact rat liver, isolated primary hepatocytes and rat hepatoma cell lines indicate that both microsomal and cytosolic epoxide hydrolases are under different regulatory control and that multiple forms of the microsomal enzyme exist.